1. Field of the invention
The present invention relates to a flange which is mounted on one end of a drum such as a photoconductor drum used in an image forming apparatus such as an electrophotographic copying machine or the like, and more particularly to a flange for a drum, which is mounted on a prescribed rotation shaft so as to rotate together with the rotation shaft, thereby transmitting the rotation of the shaft to the drum.
2. Description of the prior art
In an image forming apparatus such as an electrophotographic copying machine or the like, an image is formed using a photoconductor drum having a photoconductive layer on the outer circumferential surface thereof. The photoconductor drum is rotatably mounted inside the image forming apparatus. As the photoconductor drum rotates, a latent image is formed and developed into a visible image on the photoconductive layer of the photoconductor drum.
As shown in FIG. 5, the photoconductor drum for an image forming apparatus usually has flanges 40 and 50 mounted on both ends thereof, respectively, the flanges 40 and 50 being capable of rotating together with the photoconductor drum. That is, the photoconductor drum 20 having the flanges 40 and 50 mounted on the ends thereof rotates together with the flanges 40 and 50. The flanges 40 and 50 are provided with holes 41 and 51 passing therethrough, respectively, along the axis of rotation. The ends of a rotation shaft 30 are respectively inserted through the holes 41 and 51. Usually, the hole formed in one of the flanges (the hole 41 of the flange 40 in FIG. 5) is perfectly circular in cross section, while the hole formed in the other flange (the hole 51 of the flange 50) has an oblong cross section with opposite rounded ends (hereinafter referred to simply as "oblong cross section"). The end portions of the rotation shaft 30 have cross sections that match those of the holes 41 and 51, respectively. That is, the end portion of the rotation shaft 30 to be inserted into the hole 41 of the flange 40 is perfectly circular in cross section, while the other end portion 31 has its sides cut off to match the oblong cross section of the hole 51 of the flange 50. When the rotation shaft 30 rotates with its side-cut end portion 31 inserted into the oblong hole 51 of the flange 50, the rotation of the rotation shaft 30 is transmitted to the flange 50 via the end portion 31, so that the flange 50 is rotated together with the rotation shaft 30, which allows the photoconductor drum 20 to rotate together with the rotation shaft 30.
In the image forming apparatus, while the photoconductor drum 20 is rotating, a latent image is formed on the photoconductive layer provided on the circumferential surface thereof, the latent image then being developed with developer into a visible image. Unless the photoconductor drum 20 is mounted with its rotation axis aligned with that of the rotation shaft 30, the photoconductor drum 20 will wobble when rotated, which may cause distortion in the latent image to be formed on the photoconductor drum 20 or may prevent the latent image from being properly developed by developer. Therefore, to produce an image of good quality, the photoconductor drum 20 must be supported concentrically with respect to the rotation shaft 30. For that purpose, it is necessary to examine whether or not the photoconductor drum 20 is concentric with the rotation shaft 30 when mounted on the rotation shaft 30 in the image forming apparatus.
However, it is difficult to measure the eccentricity of the photoconductor drum 20 for rotation after the photoconductor drum 20 has been mounted in the image forming apparatus. Furthermore, in such a measurement, if it is found that the photoconductor drum 20 is not rotating concentrically with the rotation shaft 30, the photoconductor drum 20 already mounted on the rotation shaft 30 must be removed therefrom for correction, which is time consuming and thus reduces work efficiency. Therefore, the eccentricity of the photoconductor drum 20 for rotation is usually measured by rotating the photoconductor drum 20 with the flanges 40 and 50 mounted on the ends thereof while the centers of the flanges 40 and 50 are being supported by appropriate means, but without mounting the photoconductor drum 20 in the image forming apparatus.
The eccentricity of the photoconductor drum 20 for rotation is measured in the following manner: A conical rotation pin is inserted into each of the holes 41 and 51 of the flanges 40 and 50, so that the photoconductor drum 20 is supported by the rotation pins. When the rotation pins are rotated, the rotation thereof is transmitted to the photoconductor drum 20 via the flanges 40 and 50, thereby rotating the photoconductor drum 20. A dial gauge is placed in contact with a non-image area on each end of the outer circumferential surface of the photoconductor drum 20 to measure the eccentricity of the photoconductor drum 20 for rotation.
However, as previously described, the hole 51 of the flange 50 mounted on one end of the photoconductor drum 20 has an oblong cross section which matches the cross section of the side-cut end portion 31 of the rotation shaft 30 so that the flange 50 is rotated together with the rotation shaft 30. When the conical rotation pin is inserted into the hole 51 having an oblong cross section, the flange 50 cannot be held stably with its rotation axis aligned with that of the rotation pin. Thus, there is a great possibility that the flange 50 itself wobbles about the rotation pin when rotated. This prevents the accurate measurement of the eccentricity of the photoconductor drum 20 for rotation.